Object locating system



Jan. l1., 1949. B. M. OLIVER OBJECT LOCATING SYSTEM Original Filed Feb. 24, 1944 5 Sheeis-Sheet 1 Jan. 11, 1949-.- B, M, Omi/ER 2,459,117

OBJECT LOGATING SYSTEM Original FiledFeb. 24, 1944 5 Sheets-Sheet 2 BV @l J.

A TTOR/VE V Jan. 1l, 1949. B. M OLIVER 2,459,117

OBJECT LocATING SYSTEM Original Filed Feb. 24,v 1944 5 Sheets-Sheet 3 'CMR/NG FUR L08/NG DETECPUR T0 SIGNAL SELEC 70N FIG. J

DELAY CIRCU?l 400 YARDS RANGE :aan n q cmcu/r com INVENTOR B M OLIVER A TTORNE Y Jan. 11, 1949.

B. M. OLIVER OBJECT LOGATING SYSTEI original Filed Fab. 24; 1944 FIGS 5 Sheets-Sheet 4 A TTORNEY Jan. l1, 1949.

B. M. OUVER OBJECT I OCATING SYSTEM Original Filed Feb.. 24, 1944 VOLTAGE 5 Sheets-Sheet 5 TnANsN/TTEU F G PULsE EILGL'go/vs Fnou a RAG/o nEcE/VER 200 20/ cHa oF s-ELEGTEU TARGET OUTPUT PULSE 208 lil/ 200 T- GUT-oFF LINE ADJUSTBLE 00 CUT-OFF TIME J oN RANGE UN/r :ETT/NG |';r00 YZ0? fRAL/Gl: UN/T OUTPUT TnANsM/T'TEG PULsE y y 20 y T GUT'OFF "INE fV/ Gn/o VOLTAGE 200 205 H /Vz. Gn/o VOLTAGE Leur-GFF L/NE pfZOO/su-/ 2 R206 fV2 PLATE VoLTAGE l nANsM/TTEU PULSE Aaa ARD DELAY 4:1 /v i 200 Lv T mm' fV.\v G n/o VOLTAGE TnANsN/TrEo /Vl `GRID VOLTAGE [V5 6R10 VOLTAGE [V5 PLATE VGLTGE VULTGE AT CATHODE 0F V6 8 4V7 SELECTED JIGNL A TTORNE V Patented ne. 1'1, legs s PATENT' oFric-E OBJECT LGCATING SYSTEM Bernard M. Oliver, NewYork, N. Y., Bell Telephone Laboratories,

New York, N. Y.,

Original application February 24, 1944,

assignor to Incorporated,

a corporation of New York Y ASerial No.

523,722. Divided and this application March 19, 1945, Serial No. 583,472

3 Claims. l i

This invention relates to pulse operated circuitsl and more specifically to object locating and distance measuring systems. This application is a division of application Serial No. 523,722, filed February 24, 1944 and which issued as Patent 2,451,632 on October 19, 1948.

Radio object locating'and distance measuring systems (frequently called radar" systems) -are known in which radio frequency pulses of very short time duration (called transmitted pulses or emitted pulses) are emitted at intervals, reections thereof are received from objects upon upon which the emitted pulses impinge and the reection delay times for particular reflections are determined to provide indications of the distances of the objects from which the respective reflected pulses are received. Radar systems of the type in which the beam of the antenna is continually moved so that its axis follows or tracks the target are also known. In one such radar, a rotating wave guide scanner is turned about the axis of a paraboloidal reflector. The wave guide has an aperture which is displaced somewhat to one side of the axis so that as the scanner rotates around the axis of the reector, the axis of the radio beam describes a cone in space. When the axis of the reiiector is pointed directly at a target in space, the radio beam does not point squarely at the target and hence strikes it with somewhat less than maximum intensity. However, since the radio beam is describing a cone in space about the reiiector axis, it 'continues to project substantially the same amount of power toward the target at all positions in the scanning cycle. On the other hand, if the target moves oif the reflector axis, the beam at one part of its scan points more directly at the target while in the diametrically opposite part of its scan the beam points farther away from the target. In such a situation the echo pulses produced, each representative of the selected target. vary in amplitude at the frequency of rotation of the rotating antenna. AThe motor turning the antenna scanner at a low frequency, such as for example, 60 cycles, is known as the lobing motor and this low frequency rotationI is known as the lobing frequency. The modulation content of the Wave at the lobing frequency is a measure of the amount of angular displacement between the antenna axis and a direct linel from the antenna to the target and can be utilized to produce two signals to move the antenna through horizontal and vertical angles until the antenna -axis and the line of sight to the target coincide.

However, due to the fact that the signal wave comprising successive echoes from the same target comprises a multiplicity of pulses of comparatively narrow width separated by periods of much greater duration during which no signal is received, the modulation component at the lobing frequency is very small. In a typical radar, 480 radio frequency pulses (called the transmitted pulses or emitted pulses) are emitted each second, and each transmitted or -emitted pulse has a duration of about one microsecond. Because in this typical ca se the pulse separation is about 2000 times the pulse duration, and also because the amount of pulse amplitude modulation at lobing frequency is very small (usually not more than 5 percent) when the antenna is off target by the maximum permissible amount, it can be seen that most of the frequency compoents which account for the amplitude of the wave produced by the echoes from a particular target consist of the pulse repetition frequency and its high harmonics with small side frequencies while the component at the lobing frequency itself is verylsmall. For example, if the pulse amplitude somewhere in the abovevradar system were 50 volts modulated 5 per cent, the video signal component at lobing frequency would be less than about 1 millivolt. To amplify this component up to the required amplitude of several volts without system overload, it is necessary to lter out all components of a frequency greater than the lobing frequency. This is very difficult to accomplish without excessive phase shift at the lobing frequency.

It is an object of this invention to provide an object locating and distance measuring system employing a rotatable antenna which introduces a low lobing frequency in the received signal wave and utilizing means for transforming a wave produced from said signal wave, said wave comprising a succession of echoes from a particular target.. into a wave in which the low frequency modulation content is greatly increased.

Another object is to provide a following system utilizing the modulation of a train of short widely spaced .pulses modulated in amplitude in accordance with the position of the following element to control said position in which means areprovided for increasing the effectiveness of the modulation control.

Another object of -the invention is to provide a novel pulse transforming system for changing a series of short, distantly spaced pulses which,

as a whole, are amplitude modulated into a likenumber of relatively long closely spaced pulses forming a series of the same duration as said first series a d correspondingly amplitude modulated.

In ac ordance with the specific embodiment of this invention, chosen by way of example for purposes of illustration, there is disclosed an object locating and distance measuring system employing a wave transforming circuit which for convenience has; been called a lobing detector in asmuch as it detects or makes usable the modulation component of a wave comprising a plurality of relatively short pulses spaced apart by relatively long time intervals, said pulses being modulated at the lobing frequency. In a specific form or" the invention, the lobing detector comprises a condenser charged to a fixed potential shortly before the reception of a selected video pulse and which is partially discharged a few microseconds later by the received selected video echo signal from the target being tracked. The discharge of the condenser is thus caused to vary in amount in accordance with the modulation of the lobing frequency. This lobing frequency com-- ponent of the condenser voltage is the desired signal that is used to operate the angle 4tracking system to vary the position'of'the antenna axis so that it is on target in both elevation and azimuth, or, in other words, so that the error angle in azimuth (horizontal angle) and elevation (vertical angle) is reduced to substantially zero.

The invention will be more readily understood by referring to the following description taken in connection with the accompanying drawings forming a part thereof in which:

Fig. 1 ls a schematic block diagram of a radar system in accordance with the invention employing a wave transformeror lobing detector;

Fig. 2 is a circuit diagram of the wave transformer or lobing detector;

Fig. 3 is a circuit diagram of the signal selector used in the system of Fig. 1;

Fig. a is a circuit diagram of the delay circuit and pulse generator used in the system of Fig. 1;

Fig. 5 shows a modification of the lobing deftector of Fig. 2; and

Figs. 6, 7 and 8 are diagrammatical and graphical representations to aid in understanding the invention.

Referring more particularly to the drawings, Fig. l shows, by way of example for illustrative purposes, an automatic tracking radar system in the three coordinates of range (slant distance 'to the target from the observing station), azimuth (horizontal angle between a4 reference direction and the vertical plane containing the line of sight to the target) and elevation (the vertical angle between the horizontal plane and the line of sight to the target). Fig. 1 is a single line block diagram to show the relationship of the Various -major Velements of the system and is not intended to be a circuit diagram. It is to be understood that only elements necessary to show the operation of the wave transforming circuit or lobing detector of this invention have beenshownand that various elements of an automatic tracking radar .system in three coordinates, such as, for example, the oscilloscope and details of the range detector unit, have not been shown inasmuch as they are not necessary to explain the action of the lobing detector.

In the arrangement of Fig. 1, an ultra-high frequency pulse modulated wave is produced in a transmitter l0. The transmitter may comprise, for example, a high Voltage rectier of any suitable form which supplies about 12,000 volts t'o a suitable charging circuit or element capable of producing a still higher voltage.` After the ,the reflector axis.

4 charging voltage builds up to about 21,000 volts, any suitable rotary spark gap discharges the capacitor in the charging circuit. 'I'his discharge takes place in about one microsecond and causes the magnetron oscillator in the transmitter to oscillate for this brief period and send short pulses of radio frequency energy through a T-R box i i. to the antenna system l2. A suitable antenna system is disclosed in an application by A. P. King, Serial No. 499,450, led August 2,1, 1943 and in a corresponding British Patent 586,689, complete accepted March 27, 1947.

The antenna arrangement may, for example, comprise an open-ended circular antenna wave guide i3, the longitudinal axis of which is angularly related to the principal axis of the paraboloidal reiiector I4.. The aperture at the open end of the guide is in the focal plane of the reflector and placed a. small distance to the side of The antenna guide is connected to the T-R box by means of a stationary main transmission guide-extending perpendicularly to the refiector axis and ultra-high frequency pulse modulated waves are supplied to and collected from the guide. Means (not shown in Fig. 1) are provided for rotating the axis of the short wave guide about the reflector axis, and therefore for rotating the center of theaperture about the reector focus, whereby the axis of the maximum directive lobe describes in space a cone of substantially circular cross-section, and lobe notation is secured Without moving the reflector id. Means are also provided for moving the ar-` rangement for the purpose of aligning the refiector axis, which coincides with the axis of the directive cone, with any direction in space. This means comprises, by way of example, an azimuth motor i5 for varying the horizontal angle between the reflector axis and the line between the antenna and the target and an elevation motor for varying the vertical angle between the reiiector axis and the line between the antenna and the selected target it is desired to follow or'track.

The operation of the azimuth and elevation motors |15 and l'B is controlled'by signals from an angle tracking unit i1 to be described below. Mounted so as to rotate with the antenna scanner i3 are two low frequency generators represented by the boxes l 8 and l8-A. These two generators, which are called the lobing generators, generate sinusoidal waves at the lobing frequency, that is, the frequency of rotation of the wave guide antenna i 3 and which are 90 degrees apart in phase. These waves are applied to the respective azimuth and elevation phase detectors 30 and 3| in the angle tracking unit l1 and are used as reference WRVBS.

Radio frequency pulses emitted by the antenna i3 and reected by the reiiector I4 strike one or more objects and produce reflections or echoes therefrom which are received by the same antenna system and transmitted through the T-R box ii to the receiver I9. The T-R box may be of any desirable` type, for example that employing a Western Electric Company 70S-A tube in a resonant cavity. This tube is iilled with an ionizable gas and has a small gap therein. During reception, with the low voltages of the received energy, the gas is not ionized, the cavity is tuned to resonance and the received energy is applied to the receiver IS. During the transmission of a pulse from the transmitter i0, the voltages due .to the pulse ionize the gas, thus detuning the accedi? In the receiver i3 the received waves are heterodyned :to a convenient intermediate 'frequency and these intermediate frequency waves are amplied, detected, and applied to the signal selector 20 acircuit diagram of which is shown in Fig. 3.

Pulse energy from the transmitter I0, in the nature of a synchronizing pulse, controls the range unit 2| which is essentially a variable delay circuit or unit and produces a pulse `202 v (see Fig. 8-B) of predetermined length a controllable period of time after the initiation of the pulse from the transmitter I0. A suitable range is disclosed in an application of L. A. Meacham, Serial No. 491,791, illed June 22, 1943 and which issued as Patent 2,422,204 on June 17, 1947. The output pulse from the circuit 2| is applied to a delay circuit and pulse generator 22 which, for example.

produces a pulse 2|2 (see Fig. 8I) which has a shown in Fig. 8F, corresponding to a range of 400 yards from the start of the pulse in the range unit 2|. The unit 22 is shown in Fig. 4 and Awill be described more fully below. The output pulse from the range unit 2| is also applied to a range tracking unit 23 which is mechanically coupled (this connection being indicated by the dash line between the units 23 and 2 I) to the range unit 2| to vary a condenser therein in such a way as to vary thetime each output pulse in the range unit is delayed from the corresponding unit pulse from the transmitter i0. Inasmuch as the present invention does not relate to automatic range tracking no details are given herein of the range tracking unit but reference is made' to a copending application of B. M. Oliver, Serial No. 523,721, filed February 24, 1944 which shows, by way of example, an arrangement utilizing signals from a signal selector and pulses from a range unit to produce a voltage which drives a motor in one direction or the other to vary thedelay period in the range unit in such a manner that the target is tracked in range.

The delay circuit shown in Figa produces a puise, called a clearing out pulse to be described more fully below, which is applied to the device shown in Fig. 2 and which, for convenience, will be designated the lobing detector." A selected portion of the video signal from the receiver is taken from thesignal selector 20 and applied to the input of the lobing detector as indicated in Fig. 2. This input (as shown in Fig. 6) comprises a plurality of relatively short echo pulses 29| (all from lthe same target) separated Aby relatively long intervals 220 of practically no signal energy.

If the antenna is said to be on-target, that is, if its reilector axis passes through the target, all of the pulses 20| will be of substantially the same amplitude but if the antenna is' not aimed directly at the target, the received pulses 2M from the selected target will be stronger in one position of the antenna than in another due to the fact that the lobe is highly directional. The pulses 28| will under these conditions have an envelope at the lobing frequency which, for example, is 60 cycles. For an arrangement wherein 480 pulses followed by the movement ofthe antenna reflector axis. It will be apparent from a consideration of Fig. 6 that the modulation content at the lobing frequency of 60 cycles is very small being equal to the direct current component of the signal frequency and the utilization of such information to aim the antenna. The lobing detector 2 4 produces a. substantially sinusoidal wave at the lobing frequency which is amplified by the ampliner 25 and applied to both the azimuth phase detector 3U and the elevation phase detector 3| of the angle tracking unit |1. There signals are produced which are applied (through amplifiers 3S and 31, respectively) to the motors I5 and I6 to drive these motors in a direction to align the axis of the antenna with the line of sight vto the selected target both in azimuth and elevation. Before going into a detailed description of how the output wave of the lobing detector 24 is produced and the manner in which it is utilized in the rest of the angle tracking unit I1 to control the azimuth and elevation motors I5 and i6, respectively, reference will be made to Figs. 2, 3 and 4 which are circuit diagrams of the elements 2A, 20 and 22, respectively, represented by boxes in the system of Fig. 1.

Reference will rst vbe made to Fig. 4 which discloses a circuit 22 for producing a pulse 2|2 (see Fig. 8-I) which has a duration corresponding to a range of 400 yards and the initiation of which is delayed by a period of time corresponding to a range of 400 yards after the initiation pulse from the range unit 2i. 'This circuit also l produces the "clearing out pulse 206 (see Fig.

i imately 300 volts.

8E) for the lobing detector 2d. The circuit 22 -comprises tubes Vl, V2, V3, Vd and V5, the rst three of which make up the so-called delay circuit and the last two of which form the pulse generator for generating the delayed pulse 2li having a duration corresponding to e0() yards range. The function of the delay circuit coni'- prising the tubes Vl, V2 and V3 is to produce a pulse 208. 4

The range unit output pulse, shown in Fig. 8-B as the pulse 202, is applied to the control element of the tube Vi through resistor a grid leak resistor 42 being connected in the circuit between the control element and ground. The cathode is connected directly to the suppressor grid and to ground through the parallel connected resistor 43 and condenser le to apply biasto the grid. The cathode is placed at a positive potential with respect to ground by means of a voltage-dividing potentiometer comprisingl resistances 43, 45 and 46 while the screen grid is placed at positive potential with respect to ground by means of theresistor 46 which is connected to the positive terminal of a, source 41 of approx- The negative terminal of the source 4l is connected to ground. The screen grid is also connected to ground through the condenser 48. lThe anode is connected to the positive terminal of `the source lll through resistor 49 and is connected to the control element of the tube V2 through condenser 50 and resistor 5|.l Between the common terminal of the elements.

50 and 5| and ground is a tuned circuit T oo mcapacity' member 53 of a few rmcromicrofarads.

The cathode of the tube V2 is connected directly t'o ground and to the suppressor grid. The screen grid is connected through the resistance member 513 to the positive terminal of the source 4l and throughthe condenser 55`to ground. The anode of the tube V2 is connected through the resistors 56 and 6l to the positive terminal of the source 4l, the common terminal of resistances 56 and 5l' being connected to ground through the condenser 58. The anode ofthe tube V2 is .connected by means of a connection 59 to the lobing detector 24 shown in Fig. 2 and through a condenser 60 and a resistance 5I to the control .element of the tube V3, a resistor 62 being connected between the lcommon terminal of the members 60 Vand Si and ground. The cathode 'of the tube V3 is connected directly to' ground and to the suppressor grid while the screen grid is connected to the positive terminal of the source il through the resistor 63 and to ground through the condenser Eid-A. The anode of the tube V3 in Fig. 8-C.V The condenser 50fhas lbeen vcharged is connected through the' resistors 64 and 65 to the positive terminal of the source 4l, the com- 'mon terminal of the members 64 and 65 being connected to ground throughthe condenser 66.

The anode of the tube V3 is also connected to the' control element of the tube V4 through the condenser tl and the resistance 60, the common terminal of the members 6l and 68 being connected to ground through the leak resistor 69.v The cathode of the tube V4 is connected directly to the suppressor grid and through the parallel-connected resistance member i and condenser'li connected to ground through the condenser 13. v

The anode of the tube V4 is connected to the positive terminal of the source 47 through the resistor ld and is connected to the control element of the tube V through condenser l5 and resistor the common terminal of these last two members being connected to ground through the tuned circuit T' comprising the parallel-connected inductance member l'l and the adjustable condenser 'it of only a few micromicrofarads. The cathode of the tube V5 is directly connected to the suppressor grid and to ground. The screen grid is connected to the positive terminal oi' the source Si 'through the resistor 19 and is connected to ground through the condenser 8|). The anode oi' the tube V5 is connected to the positive terminal of the source dl through the resistors ti and t2, the common terminal of these last two members being connected to ground 'through the condenser 83. The anode of the tube V5 is also connected through the coupling condenser 84 to the control element of the tube V6 in Fig. 3.

The operation of the circuit arrangement in Fig. 4 will now be described. The grid of the tube Vi is biased below cut-olf because oi. the connection of the cathode to the positive ,terminal of the source 47 through the voltage divider comprising the resistances 43, 45 and 46. When the pulse 202 is applied to the tube Vi, it conducts plate current for the instant that this grid is above the cut-ofi voltage. The cut-off line 203 is shown trol grid causes the plate voltage of this tube' from the 30G-voit B supply through the resistor 49. When VI draws platel current `during the pulse, condenser 53 is suddenly charged negatively through the path comprising condensers 4d and 50 and tube VI. The lplate voltage drop is about200 volts and the grid' ofthe tube V2 is driven negative by the same amount. The L-C network T begins an oscillation which is quenched after one-quarter cycle because the voltage across it begins to swing positive and the grid of the tube V2 begins to draw current. The oscillatory voltage has practically the same form as the pulse 204 shown in Fig. 8-D which is lthe grid voltage curve of the tube V2. The cut-off line 205 for the tube V2 is also shown in this gure. The large negative grid voltage 204 .applied to the grid of tube V2 cuts od this tube for a length of `time equal to one-fourth of the period of one oscillation of the network T and produces a plate voltage wave having the shape shown in Fig. 8-E. The sloping sides of this wave are caused by the condenser 80 and the total stray capacity of the lead 59 shunting the resistor 56 but do not interfere with the operation of the lobing detector circuit to which this wave is applied by means of the connection 59. The grid of the tube V3 is coupled to the plate of the tube V2 through the 10-micromicrofarad condenser B0. This condenser and the TIG-ohm resistance 62 have a very short time constant and differentiate the plate voltage wave produced on tube V2 to a form shOwn in Fig. 8-F, the pulse 2M in 'this gure being delayed from the pulse v202 by a time interval corresponding to substantially 400 yards range. The differentiated pulse 20W is amplified and changed in polarity by the tube V3 to produce a pulse 208 having the -wave form shown in Fig. 8-G. This output is applied to the grid of the tube V4 which is biased below cut-oil by connecting its cathode to the B voltage supply 41 through the voltage divider arrangement comprising the resistances 11|,l 'HA and l2. The positive pulse 208 applied to the conto drop suddenly (obviously the negative pulse 209 has no effect on the tube). Network T starts to oscillate, but the oscillation stops at the end of one-quarter cycle when the grid of the tube V5 .begins to swing positive and draw a grid current. The operation of the tube V4 is similar to that of tube Vi except that its grid pulse has been delayed lby the time of one-quarter cycle of an oscillation of the network T (corresponding to 400 yards range). The lgrid voltage wave 2l`0 of the tube V5 is shown in Fig. 8-H. Tube V5 is cut off by this large negative grid voltage and produces an output voltage pulse 2l2 similar to that shown in Fig. 8 1. This voltage is applied to the grid of the tube V6 inthe signal selector circuit shown in Fig. 3. The length of the pulse 2i2 shown in Fig. 8-I corresponds to a range of approximately 400 yards and it starts after a time interval corresponding to a range of approximately 400 yards after the range unit pulse 202 shown in Fig. 8-B. 'I'he length of the pulse produced by the pulse lgenerators V4 and V5 may be adjusted by means of the condenser 18.

Reference will now be made to Fig. 3 which shows tubes V6 and V1 and their associated circuit connections which comprises a suitable signal selector 20. The output pulse 2I2 from the tube V5 of Fig. 4 is applied to the control grid of the tube V6 through the coupling condenser B4 and the resistor 85, the common terminal of these last two elements being connected to ground through the resistor 86. The cathode of the tube V6 is connected to ground through a resistor 81 and is also directly connected to the suppressor grid. The anode and screen grid of the tube V6 are connected to the positive terminal of the source 41 through the resistor 88 and to ground through the resistor 89 which is shunted bya condenser 90. Tube V6 serves as a cathode follower, the output connection being made from the cathode of the tube V8 to the cathode of the tube V1. The video signal from the receiver I9, shown by Fig. 8-A and comprising for each transmitted pulse cycle a pulse 200' representative of a transmitted pulse and one or more pulses which are reflections or echoes from the targets (the pulse representing the target to be followed being designated by the reference character 20 I) is applied to the control grid of the tube V1 through the coupling condenser 9| and the resistor 92. The common terminal of the members 9| and 92 is conneoted to ground through the resistor 96A. The cathode of the tube V1 is connected to the suppressor grid thereof While the screen grid is connected to the positive terminal of the source 41 through the resistors 93 and 90, the common terminal of these two resistors being connected to ground through the condenser 95. The output from the signal selector 20 shown in Fig. 3 to the lobing detector of Fig. f is taken from the screen grid of the tube V1 through the connection 96. The anode of the tube V1 is connected to the positive terminal of the source 01' through resistors 91 and 98, the common terminal of these resistors being connected to ground through the condenser 99. The anode of the tube V1 is connected to an amplifier |00, the output of which is applied to the range tracking unit 23. The manner in which such a selected signal is utilized for range tracking is described, by way of example in the copend- -ing application of B. M. Oliver, Serial No. 523,721,

led February 24, 1944.

The operation of the signal selector shown in Fig. 3 will now be described. This circuit, acting as a gate, permits only those signals which occur Within a certain small range (time) interval to be passed on to operate the automatic ranging equipment which includes the range tracking unit pulse 2 I4. In the operation of ther-ange tracking unit 23, as described, for example, in the copending application of B. M. Oliver, Serial No. 523,721, nled February 24, 1944, the range unit is controlled from the range tracking unit 23 in such a way that the output pulse from the range unit occurs at a time which will cause the pedestal pulse 2H -to bracket the echo pulse 20| corresponding to the selected target. The output of the signal selector 20, which is applied to the tube V8 of the lobing detector 24 shown-in Fig. 2 by means of the connection 98, the condenser |0| and the resistor |02, and to the control element of the tube V9 thereof through the elements 96, |0I and |03, is shown in Fig. 8-K. As shown in this figure, only those video signals within the time span of the pulses 2I2 pass through the signal selector. The tubes V8 and V9 are connected in parallel so as to amplify the signals applied to their control elements. The two cathodes are connected together and each is connected to ground through resistors |00 and |05 in series, thelatter of which is adjustable. The condenser |06 is connected in parallel with the series-connectedcircuit comprising the elements |04 and |05. The anodes of the tubes V8 and V9 are connected together and through the anode-cathode path of the tube V10 to the positive terminal of the source 41. The cathodes of the tubes V8 and V9 are placed at a positive potential by means of the voltage divider comprising the resistors |05, |04 and |01. The cathode of the tube VIO is connected to ground l through the condenser |08. The control element 23 and the lobing detector 24 the output of which is used for automatic angle tracking. In this process of selection, video signals from the receiver I 9 represented in Fig. 8-A are combined with the 40G-yard pulse 212 which is present in the output of the tube V5. The combination of these two is effected in the tube V1. The pedestal pulse 2 I2 having a 40G-yard width and a 400-yard delay behind the range pulse 202 obtained at the plate of the tube V5 is applied to the grid of the tube V6. The cathode current and voltage across the cathode resistor-81 follow the voltage applied to the grid of this tube. The positive potential across the resistor 81 is also applied to the cathode of the tube V1 since the resistor is common to both circuits. This has the effector placing a more negative bias on the grid of the tube V1 during the application of positive pulses 2I2 to the grid of the tube V6. The incoming video sigof the tube VIO is connected-by means of the. resistor |09 and the connection 59 to the anode of the tube V2 in the delay circuit shown in Fig. 4. The potential appearing across the condenser |08 is applied through resistance I|0 to the control grid of the tube VI I, this grid being connected to ground through the condenser I I. The cathode of the tube VI I is connected to ground through the resistor II2 and the anode of the tube VII is connected directly to the positive terminal of the source 01. 'Ihe lobing output wave is taken from across the resistance II2 through the coupling condenser IIS. f

The operation of the lobing detector will now be described. The lobing detector, as indicated in the system of Fig. 1, is part of the angle tracking unit I1. Its function is to extract the cycle lobing frequency from the selected receiver video signal and pass this frequency to the rest of the angle tracking unit. Referring to Fig. 6, the pulses 20| correspond to the pulses 20| in Fig.

8-K, there being one of these pulses for every,

transmitted pulse and thus they are approximately 2082 microseconds apart. There is no signal energy in the wave between the pulses 20|. If the antenna I2 does not have its reflector axis aimed at the target, the pulses 20| will lie under a 60- cycle sinusoidal envelope, there being one complete cycle of the (iO-cycle lobing frequency for every eight pulses, or in other words, for every complete rotation of thewave guide I3 eight pulses will be emitted. If the antenna axis is off-target the pulses emitted at some points of the rotation of the antenna will, because of the highlydirectional sensitivity of the antenna, produce a larger amplitude echo pulse 20| than others and the envelope 22| will be a sine wave the amplitude of which and the phase of which (with respect to the two reference waves generated by the 60-cycle generators I8 and IB-A) can be used to generate signals to center the antenna with respect to the target. Inasmuch as 11' the wave of Fig. 6 has a low modulation content at the lobing frequency, the lobing detector is essentially a wave transformer as it produces an output wave. such as that shown in Fig. 7, which has a. much larger modulation content at the lobing frequency. Referring now to Fig. v2, the grid of the tube VIO is connected to the plate of the tube V2 in the 40G-yard delay circuit, and the large positive plate voltage pulse 206, Fig. S-E, carries the grid of VIO positive, beginning with the start of the range unit pulse 202 and lasting for the 40G-yard delay interval. The condenser |08 in the cathode circuit of the tube VI 0 charges during the period that the grid of this tube is carried positive by the pulse 206. When the grid voltage decreases, the tube V| is cut off and the condenser- |08 remains charged. The above charging action occurs immediately after the range unit pulse 202. The selected signal shown above the cut-oi line 2|5 in Fig. 8K and which is applied to the tubes V8 and V9 in parallel occurs after the range unit pulse 202 by a time equivalent to the 40G-yard delay interval plus one-half the 40G-yard range pulls 2I2, or 600 yards. It follows then that the condenser |08 will have been charged and left at its maximum potential (represented by the line 222 in Fig. 7) before the video signal is applied to the lobing detector by means of the connection 98. The cathode bias of the tubes V8 and V8 is adjusted so that only signals on top of the 40G-yard range pedestal 2|1 in Fig. B-K cause the tubes V8 and V9 to conduct. Since the ungrounded side of the condenser I 08 is connected to the plates of the tubes V8l and V9, this condenser ispartially discharged when the selected signal oi.' Fig. 8K causes plate current to ow in V8 and V8. The amount by which the condenser |08 is discharged isY dependent upon the amount of plate current.

flowing in the tubes V8 and V9 and therefore upon the amplitude ofthe signal pulse applied to the grids thereof. If the antenna is not pointing exactly at the target, the amplitude oi' the selected echo pulses from the receiver will vary at the lobing frequency (as explained above in connection with Fig. 6) and the potential to which the condenser |08 is discharged will vary from pulse to pulse at this same rate. After the condenser |08 is partially discharged, it maintains this value of charge until it is again charged at the time of The lobing detector 24 delivers to the two phase detectors and 3| a constant voltage if the antenna is on-target" or. if it is not on target, a (iO-cycle voltage whose amplitude and phase indicates the antenna pointing error. If the antenna is pointed directly at a target, as pointed out above. all reflected pulses will be of the same magnitude because the antenna beam, or lobe, will sweep around in a cone, the axis of which will pass through the target. Under this condition, there will be no modulation of the video signal and a constant voltage only will be delivered to the azimuth and elevationv phase detectors 30 and 3|. If the antenna is not pointed directly at the target, stronger echoes will be received from lobes nearer the target than from those further away and since the speedof the lobe switching motor, that is, the motor (not shown) rotating the wave guide I3, is, for example, 3600 revolutions per minute, this results in a 60-cycle per second modulation of the reflected signal. It is the function of the rest of the angle tracking unit I1 to transform the 60cycle lobing input into control voltages to drive the azimuth and elevation motors I5 and I6, thus changing the position of the antenna so that it will point directly at the selected target. Actually two control voltages are developed: one proportional to the antenna error in azimuth and one proportional to the antenna error in elevation. The amplitude and polarity of each control voltage denotes the magnitude and direction of the corresponding antenna pointthe next range unit 202 pulse. The voltage onl the condenser |08 will have a wave shape similar to that shown in Fig. 7, and will have a large lobing frequency component as indicated by the dotted line 223 which is drawn through the midpoints of horizontal line 224 representing the voltages to which condenser |08 is by the successive pulses. Th

tween two successive transmitted pulses or 1,660 of a second. This .corresponds to a phase delay of about 22% degrees (with 8 pulses per scan) which is compensated by shifting the phases of the reference waves from the generators I8 and |8A as will be pointed out below. The voltage across the condenser |08 is applied through the resistor IIO to the grid of the tube VII which operates as a cathode follower output tube. The low-pass filter action of the resistor I I0 and the condenser III reduces the spikes 225 of the wave shown in Fig. 7 and a signal is produced (if the pointing error is large) like the typical signal 226.shown in Fig. 1. This signal is amplified in any suitable ampliiier 25 and applied to the azimuth and elevation phase detectors 30 and 3|.

partially discharged is component 223 has a. time delay of about one-half the interval be 1 ing error.

As shown in the block diagram of Fig. 1, the modulated and amplified echo pulses are applied to the azimuth andelevation phase detectors 30 and 3|, respectively. Two 60cycle voltages 221 and 228, balanced with respect to ground and which are degrees out of phase with each other, are obtained from the two Gil-cycle generators I8 and |8A (if desired, the members I8 and I8-A can be a single two-phase generator) are used as reference waves for determining the instantaneous position of the antenna lobe. The azimuth reference wave 221 would normally have a maximum when the axis of the antenna beam is at its maximum horizontal displacement from the reector axis and the elevation wave 228 would normally have a maximum when the axis of the antenna beam is at its maximum vertical displacement from the reflector axis were it not for the phase shift produced by the lobing detector.

Because of this phase shift, the phases of the reference waves are shifted accordingly to compensate for it. One voltage 221 is applied to the azimuth phase detector 80 bylmeans of the connection |20 and the other reference voltage is applied to the elevation phase detector 3| by means of the connection I2I Each phase detector produces an output voltage which is proportional to the component in phase with its particular reference carrier wave. Any suitable phase detector may be utilized; for example, reference is made to the double tube arrangement in Patent 1,539,903, issued June 2, 1925, to L. M. Ilgenfritz for producing such a voltage component. The phase detector 30 comprises, for example, a double vacuum tube circuit wherein the grids of both tubes are varied in potential at a phase difference" of degrees by means of the reference wave 221 while the wave 226 is applied to the grid-cathode circuit of both tubes in the same phase. If the phase displacement between waves 228 and 221 lis zero or 180 degrees (called the in-phase condition) a maximum signal is produced in the output i3 circuit of the phase detector. A lobbing signal 90 degrees or 270 degrees out of phase with the reference frequency wave 221 results in no signal voltage in the output circuit. If the phase of the lobing signal is between these two conditions, the output will be a signal voltage, theamplitude of which is somewhere between zero and the maximum obtained for the in-phase condition, depending on the phase diierence. The elevation phase detector 3| is similar to the device 30 except that the reference wave 228 is applied between the grids ofthe two tubes so that the voltages of the grids are 180 degrees apart instead of using the wave 221 in this manner as in the device 3U. The

same lobing signal 226 is applied to both the azimuth and elevation phase detectors, b ut since the Gil-cycle reference waves 221 and 228 for these two detectors are 90 degrees out of phase with each other, the resultant voltages will change in different manners. For example, when the lobing frequency is in phase (or 180 degrees out of phase) with the azimuth reference Wave 221, it will be 90 degrees out of phase with the elevation reference wave 228. This means that for this condition a signal voltage will be produced for controlling the azimuth circuit but no voltage will be produced in the elevation circuit. Obviously, for other conditions, signals representing errors in both azimuth and elevation will be produced in the output circuits of the devices 30 and 3|.

The outputs of the phase detectors 3U and 3| after being amplified by the devices 32 and 33 are applied to the modulators 34 and 35, respectvely. each of which may be, for example, of the copper-oxide bridge type disclosed in Patent 2,025,158 issued December 24, 1935 to F. A. Cowan. Also connected to each of these modulators is a 60-cycle carrier wave derived from the power line and a phase shifting network 35A connected to the source 38. With no direct current input to each modulator, no Gil-cycle voltage appears in the modulator output. When a signal voltage is applied to the modulator 3d, for example, there appears at the modulator output a proportional ISO-cycle voltage which either leads or lags the voltage of the source 38 by 90 degrees, depending on the polarity of the signal voltage. The outputs of the modulators 3a and 35 are applied to ampliers 36 and 31, respectively, and the outputs of these two ampliers are applied to the azimuth and elevation motors I and I6, respectively, to drive the antenna until it is ontarget and thereby reduce the azimuth and elevation error voltages to zero.

Fig. 5 shows a modification of the arrangement shown in Fig. 2. In Fig. 5 portions to the left of the line X-X are intended to be the same as the portions to the left of the line X-X in Fig. 2 so they have not been reproduced in this figure. Moreover, in Fig. 5 all elements having the same reference characters as the corresponding elements in Fig. 2 are similar and operate in a similar manner. The arrangement of Fig. 5 diiers from that of Fig. 2 in that the average potential of the heater for the cathodes in the tubes VIO- and V|| is made to follow the potential of the cathode of VII). This is accomplished by means of the equal resistors |30 and |3I, the corn- Inon terminal of which is connected through resistor |32 to the cathode of the tube VII and through resistor |33 to ground. Resistors |32 and |33 serve as a voltage dividing potentiometer, their common terminal being at a potential less than the cathode of VII by an amount equal to the'bias across that tube and hence at the potential of the grid of YH andthe cathode ofing oli during the interval between pulses and` thereby producing an inaccurate output signal from the lobing detector.

Since the amount by which the condenser |08 is discharged each cycle is proportional to the selected signal pulse strength, the average potential of this condenser and hence of the cathode of V|| will be less, the greater the average selected signal strength. This variation in potential can be used to control automatically the receiver gain by well-known automatic gain control methods in such a manner as to hold the average selected signal strength substantially constant over a wide range of receiver input.

The circuit constants of an operative form of the invention have been indicated on the drawing but it is to be understood that the invention is not limited to the use of these specific circuit constants as a change of one or more of the variables of the system may necessitate a change of the circuit constants in a manner understood by all those skilled in the art.

Although the present invention has been described in terms of various illustrative embodiments it should be realized that the invention and its several features are susceptible of embodiment in a wide variety of other forms. Hence the invention is to be understood as comprehending such other forms -as may fairly come within the spirit and letter of the appended claims. For example, the wave transforming circuit designated the lobing detector is not limited to use in radar systems but may be used in any arrangement wherein it is desired to produce a wave of the general form shown in Fig. 7 from a wave of the general type shown in Fig.` '6. Moreover, while in the arrangements of Fig. 2 and Fig. 5, the condenser |08 is charged by the clearing-out pulse and discharged by the incoming d echo pulses, it is obvious that in a modification,

the condenser |08 can be discharged to a reference potential and then charged by an amount depending on the amplitude of the echo pulse. In another modication, the clearing out pulse can be caused to return the condenser |08 to a potential which is not constant butrather varies in accordance with some modulation which it isl desired to combine with the received signal. In the claims, the term reference level is intended to mean either a constant potential or one which varies in a desired manner.

What is claimed is: 1. In combination, a rotating element the axis of which 'it is desired to keep aimed at an object, means including said element for forming a voltage Wave comprising a plurality of short pulses of varying amplitude but of the same polarity spaced apart by time intervals which are long compared to the duration of a pulse, said voltage wave having a low frequency envelope, means for generating two reference waves by the rotation of said element, said reference waves being degrees displaced from one another and of the same frequency as the envelope in said voltage wave, separate motor means for shifting the position of the axis of said rotating element through horizontal. and vertical angles, means for modifying the said voltage wave to a wave comprising a plurality of steps, each step corresponding in amplitude to that of a pulse in said voltage 15 wave and the steps being separated by time intervals which are short compared to the duration of each step, means for comparing the phase of -said stepped wave and each of said reference 4wave comprise a storage element, means for conditioning said storage element by varying the amount of energy stored therein until it reaches a reference level before the occurrence of each pulse in said voltage wave, and means for applying each pulse to the storage element to vary the 16 amount of energy stored therein by an amount depending on the intensity of that pulse.

3. The combination of elements as in claim 1 in which each pulse in said voltage Wave is produced by reflection from the object of a radio frequency pulse transmitted from said rotating element. Y

BERNARD M. OLIVER.

REFERENCES CITED The following references 'are of record in the file of this patent:

UNITED STATES PATENTS Y Number Name Date 2,313,966 Pooh Mar. 16, 1943 2,314,029 Bond et al. Mar. 16, 1943 2,412,612 Godet Dec. 17, 1946 2,420,334 White May 13, 1947 2,421,028 King May 27, 1947 

